Andy Murray believes tennis is only 30 per cent physical and the rest psychological as he steps up his preparations for the Australian Open.

That has not stopped the US Open champion, who has twice reached the final in Melbourne, from adding another three pounds of muscle after doubling his weights sessions over the off-season.

The Scot, who met former world heavyweight champion Lennox Lewis in December, believes there is little difference between the top players in terms of ability, but the crucial distinction is how they perform under pressure.

"I watched Lennox a lot when I was growing up, so it was cool to meet him," Murray told the Daily Telegraph. "I spoke to him for maybe 45 minutes, although I had to break off to go training in the middle.

"He is a legend and heavyweight boxing is the pinnacle of sport really, especially when he was fighting. So to get to pick his brains about certain things was nice.

"I asked a lot of questions about current boxers and how you train. He was saying boxing is 70 per cent mental, 30 per cent physical in the actual talent you need, and I think that applies to a lot of sports.

"The difference in how guys hit a ball is not that huge, but it's about how you deal with the pressure moments and who can hold their nerve. When you get towards the end of sets, some guys make more mistakes than others."

Rather than rest on his laurels after landing his first major in New York last September, the success has left Murray determined to add to his grand slam tally.

"It's taken a long time to get there and to win those sorts of events," Murray said. "I know the feeling when you do win them now, and it's worth all of the work that you put in.

"In the past, there were loads and loads of questions. I wasn't physically strong enough. I wasn't mentally strong enough. I didn't listen to my coaches. I was spoilt. Whatever it was, none of that really bothers me anymore. I'm just looking for ways to keep improving."